Hydro-power reservoirs emit methane, a greenhouse gas: no free lunch?

Hoover Dam by Flickr user Airwolfhound (Used under CC License)The energy sources used to generate grid electricity can be a major source of greenhouse-gas emissions, and thus they affect the environmental impact of electric cars. The cleaner the electricity used to charge an electric car, the cleaner that car becomes in operation. And among potential energy sources, hydroelectric power from dams would seem...